Andre Luiz Pinto

Recrystallization behavior of a cold-rolled niobium bicrystal

A high-purity coarse-grained niobium bicrystal was 70% cold rolled in multiple passes. Deformation occurred in an inhomogeneous manner in both grains giving rise to a banded structure. In consequence, highly misoriented boundaries were developed in the microstructure in a wide range of misorientations, many reaching about 55°. These boundaries act as effective nucleation sites for recrystallization. The microstructure of both grains was investigated using electron backscatter diffraction (EBSD) in the cold-worked state in order to quantify the misorientations (ψ) associated to these bands. Upon annealing at 800 and 900 °C, the new recrystallized grains were nucleated preferentially at deformation heterogeneities and in the vicinity of the prior grain boundary in this bicrystal.

Analysis of Grain Boundary Character in a Fine-Grained Nickel-Based Superalloy 718

Abstract In the current work, sheets of superalloy 718 were processed via thermomechanical route by hot and cold rolling, followed by annealing below the δ phase solvus temperature and precipitation hardening to optimum strength. Grain boundary character distribution throughout the processing was mapped via EBSD and its evolution discussed. The results show that it is possible to process the alloy to a fine grain size obtaining concomitantly a considerably high proportion of special boundaries Σ3, Σ9, and Σ27. The precipitation of δ phase presented a strong grain refining role, without significantly impairing the twinning mechanism and, consequently, the Σ3, Σ9, and Σ27 boundary formations.

Analysis of ridging in three ferritic stainless steel sheets

Abstract In the present work, three types of ferritic stainless steel sheets AISI 430A (16%Cr), AISI 430E (16%Cr, 0·36%Nb) and AISI 434 (16%Cr, 1%Mo), known to display different ridging behaviours, were characterised in both microstructure and texture using optical metallography and electron backscatter diffraction techniques. It was concluded that surface microridging is a result of the differential plastic behaviour of {111}〈uvw〉 and {001}〈uvw〉 grain colonies existing in the sheet; severe ridging (undulations) is a consequence of through thickness texture and microstructure inhomogeneities that lead to grain buckling under internal compressive stresses.

An EBSD Analysis of the Origins of Ridging in AISI 430 Steel Sheets

In the present work the characterisation of both the microstructure and the microtexture of two ferritic stainless steel sheets - AISI 430 (Fe17% Cr) and AISI 434 (17% Cr, 1% Mo) - known to display different ridging behaviours, was carried out by optical metallography, EBSD and OIM techniques. It was concluded that severe ridging is a consequence of: (a) presence of {111} and {001} colonies of grains alternating throughout the sheet plane; (b) through thickness texture inhomogeneity with layers of {001}<110> oriented large grains of low Rvalues sandwiched between layers of higher R-value textured material.

Characterization of CSS deposited CdTe films by electron back-scatter diffraction technique

The properties of a material are affected by the orientations of individual grains, that is, by its microtexture. Microtexture can be determined in a scanning electron microscope by analyzing the electron back-scatter diffraction patterns provided by the specimen. This work focuses upon microtexture determination in cadmium telluride thin films deposited by close spaced sublimation. The texture of individual grains, the misorientation between grains, and coincident site lattice boundary maps were obtained, showing that electron back-scatter diffraction is a useful technique for investigating grain boundary features in these films.

Micromechanisms Involved in Grain Boundary Engineering

Grain boundary engineering has been applied to different materials in order to increase properties particularly sensitive to intergranular phenomena. This work analyses the micromechanisms that allow the control of the amount of special boundaries which respect coincidence site lattice theory. α-brass, a lead alloy, Inconel 625 and Inconel 600 were submitted to different thermomechanical treatments and were analyzed via electron backscatter diffraction in order to characterize their grain boundaries. The occurrence of thin twins in some crystal directions during the deformation step seems to determine the results obtained as well as strain induced boundary migration.